Civil Engineering Reference
In-Depth Information
apart. Our top boxing is made up of three pieces of 90 × 45 pine, two pieces vertical
nailed to the third piece which is horizontal, fitted flush with the underside of the vertical
timbers (see Figure 4.6). The vertical timbers are nailed to the horizontal timber with
75 mm nails at approximately 200 mm centres. A spacer block of 90 × 45 approximately
100 mm long is fitted in the top of the bale boxing between the two vertical timbers to
prevent the top of the boxing being squeezed together during compression. When
building load-bearing walls, these blocks would be positioned at the junction of the
rafters to the top boxing.
Figure 4.6
Top bale boxing is to be positioned centrally on top of the bale wall
By having the top boxing narrower than the bottom boxing, a triangulated pressure is
brought to bear on the wall. This applies pressure to the sides of the wall in the upper
region, adding greater strength and stability to the wall.
The top bale boxing is positioned in the middle of the bales on the top of the wall.
Flat filament polyester straps are then fitted to encircle the top and bottom boxing and
the bales contained within them. Pressure is then applied to the strapping with a
tensioning tool. Not only is the wall compressed, but the top boxing will create a slight
indent in the upperside of the top row of bales, adding greater stability to its position.
This provides greater resistance to its dislodgment by lateral pressures from weather and
when impact is brought to bear.
Compression of straw bale walls
Front-end loader
Front-end loader tractors have been used to apply pressure to the top boxing. The top
boxing is then tied to the bottom boxing using wire.
Plastic and polypropylene strapping
Standard polypropylene and plastic strapping are, I believe, unsuitable for compression
strapping as the manufacturers will not guarantee the strength of any strapping that has
